The long-term objective of this project is to arrive at an understanding of how the nervous system generates behavior and how the neuronal circuits responsible for this function arise during ontogeny. The experimental material on which these studies are to be carried out is the nervous system of leeches, the class of blood-sucking worms belonging to the annelid phylum. The immediate research objectives are as follows: 1) We plan to continue the analysis of the neural subsystem that controls the leech heartbeat, and to ascertain how its oscillatory rhythm is generated, how it is modulated physiologically, and whether it shows plasticity. 2) We plan to continue the study of the leech photosensory systems, and to establish the receptive field structure and stimulus dependence of higher order sensory neurons, in the hope of relating neurophysiological data to light-induced behavioral acts. 3) We plan to embark on an anatomical and electrophysiological study of the embryological development of the leech nervous system. For this purpose we will first attempt to start laboratory culture of a suitable leech species, probably Glossiphonia. BIBLIOGRAPHIC REFERENCES: J.R. Kretz, G.S. Stent and W.B. Kristan, Jr. Photosensory input pathways in the medicinal leech. J. Comp. Physiol. 106: 1-37, 1976. W.B. Kristan, Jr. and G.S. Stent. Peripheral feedback in the leech swimming rhythm. In "Cold Spring Harbor Symp. Quant. Biol." 40: 663-674, 1976.